中国东部断陷湖盆细粒沉积岩岩相划分方案探讨--以渤海湾盆地南部古近系细粒沉积岩为例

Classification Scheme for Lithofacies of Fine-Grained Sedimentary Rocks in Faulted Basins of Eastern China:Insights from the Fine-Grained Sedimentary Rocks in Paleogene,Southern Bohai Bay Basin

细粒沉积岩岩相研究是烃源岩和页岩油、致密油储层研究的重要基础,鉴于我国陆相断陷湖盆环境多变和细粒沉积岩类型多样、岩石组合类型复杂的特点,需要进行细粒沉积岩岩相分类。以渤海湾盆地南部古近系细粒沉积岩发育段为研究对象,通过厘米级岩芯观察描述、岩石薄片鉴定、激光共聚焦显微镜观察分析等技术,研究细粒沉积岩基本特征。陆相断陷湖盆细粒沉积岩岩相划分可以按照(1)宏观岩芯精细观察描述,归纳垂向岩石类型组合;(2)分析沉积微环境;(3)对不同岩石类型组合进行X射线全岩矿物衍射和TOC测试,划分岩石类型和岩相大类;(4)微观镜下剖析纹层叠置关系;(5)分析成因和形成机制,对岩亚类细分等5步进行。岩相大类划分要简洁,是为满足油田勘探工作易于操作、建立与常规测井资料之间关系等要求;亚类细分是便于研究微观源储关系、分析沉积微环境和储层微观结构等。

The lithofacies study of fine-grained sedimentary rocks is an important foundation for better understanding hydrocarbon source rocks and tight oil and shale oil reservoirs. Considering the variety of downfaulted basin environments, multiple types of fine grained sediments and complex of rock assemblages in China, it is highly necessary to carry out lithofacies classification for fine-grained sedimentary rocks. Paleogene fine-grained sedimentary rocks in Bohai Bay Basin was taken as a study objective to probe the basic features of fine-grained sedimentary rocks through description of centimeter-level cores, identification of thin sections using a confocal laser scanning microscope, and analysis of whole rock X-ray diffraction. Lithofacies of fine-grained sedimentary rocks in continental faulted basin can be classified based on the following （1） vertical rock assemblage types summarized by detailed description of core; （2） analysis of sedimentary micro-environment; （3） rock types and lithofacies grouping of different rock assemblage types using whole rock X-ray diffraction and scanning electron microscopy technology; （4） superimposition relation under microscope; and （5） genesis and forming mechanism of lithofacies. Our classification for lithofacies can meet oilfield prospecting requirements that are easy to conduct facies classification and establish the relation between rock types and logging data. And sub-group classification can also facilitate analyses of the relation between source rock and reservoir, micro-environment of sedimentation, and microscopic structure of reservoirs.